1. Field of the Invention
The invention relates to friction clutches and brakes of the type in which a single surface electromagnetic clutch has an annular armature disposed coaxially with a torque translating means interposed an input and output means. The armature being relatively displaceable in the axial direction of the clutch or brake, engagement of the torque translating means being initiated upon the energization of the electromagnet so as to attract the armature.
2. Description of the Prior Art
Electromagnetic clutches or brakes as used heretofore generally have an input or driving means coaxially disposed with respect to an output or driven means. Interposed said driven and driving means is a friction means utilizing frictional surfaces to translate the torque from the input or driving means to the output or driven means. This frictional torque transmitting arrangement is generally obtained through a series of annular plates or discs with frictional material mounted to the outer periphery of the plate. These plates are by some means axially displced to enable the frictional material portion of the plates to come into contact with each other thereby either translate torque from the input to the output means in the case of a clutch, or to absorb torque in the case of a brake arrangement. The axial movement of the friction plates or discs is accomplished directly or indirectly through the use of a plurality of spherical members located in a depression within the friction plates. Relative angular movement between the pressure plates causes the ball to follow a directed path along this depression resulting in the pressure plates moving in an axial direction thereby allowing the frictional surfaces at the outer periphery of the plates to come into contact with one another and providing a clutching or braking action. In all of the prior art embodiments, the spherical members are utilized to obtain axial movement of the friction plates and the axial movement of these friction plates causes the frictional surfaces to come into engagement and thereby, through these frictional surfaces, a torque is translated from the input to the output means. Such prior art as U.S. Pat. No. 2,866,528 by J. W. Jacobs, entitled "Clutch for Refrigeration Apparatus"; 2,801,719, by R. D. Clark, entitled "Electromechanically Actuated Friction Brake or Clutch"; and 2,161,359 by H. T. Lambert, entitled "Brake Construction"; are examples of where a plurality of spherical members located in a pre-defined depression are used primarily as a means of obtaining axial displacement of an arrangement of annular plates to obtain a secondary clutching or braking action through engagement of mutually opposing frictional surfaces, yet the spherical members are not required to contribute significantly to the translation of torque from the input to the output means. The basic reason for the prior art avoiding the use of the spherical members to translate torque in clutches or brakes is the fact that it is well known in the art that a spherical member riding between two inclined planes can easily lock up or freeze and thereby prevent the torque carrying device from disengaging. It is because of this past problem that the prior art has chosen to rely on a secondary frictional arrangement, namely, the mutually opposing frictional surfaces of the annular plate members to transfer or absorb torque as shown by the prior art. Further, because of this prior identified problem, some of the prior art has attempted to avoid this problem by constructing the depressions in such a way whereby the spherical members are forced to move in a single specific direction of rotation and thereby avoid the lock up problem. This is exhibited in FIGS. 2 and 3 of U.S. Pat. No. 2,866,528. In other cases, such as U.S. Pat. No. 2,801,719, a locator plate is utilized to guide the spherical members in circular holes and prevent the spherical members from assuming a position on the inclines of the depressions that would cause the brake or clutch assembly to lock up and thereby prevent the frictional surfaces from disengaging. Other prior art such as U.S. Pat. No. 2,161,359 utilizes a series of compression springs to insure that after the spherical members perform the function of causing axial movement of the frictional plates, the spherical members do not lock up and return to their initial position. This configuration, of course, affects the torque output of the clutch or brake in that the force generated by the compressed coil spring must be overcome before the frictional surfaces can be engaged and, also, this force opposes the clutching force.